Heat exchanger obtained from aluminum or aluminum alloy

ABSTRACT

Provided is a heat exchanger including a heat exchange fin in which frost formation at the time of heater operation can be prevented to the extent possible, and under such a condition that condensation is liable to occur on a fin surface, a water droplet of condensed water can be quickly removed by bringing the water droplet into contact with a hydrophilic film, and as a result, a favorable heat exchange function can be continuously obtained without any increase in ventilation resistance. The heat exchanger includes a heat exchange fin made of an aluminum plate material that has a crosslinked hydrophobic film having a frost formation-suppressing effect and a hydrophilic film, in which: an area occupied by the crosslinked hydrophobic film in a square area measuring 10 mm by 10 mm at an arbitrary position on a surface of the heat exchange fin is 20 to 80%; and the crosslinked hydrophobic film is formed of an aqueous hydrophobic coating composition containing a resin (A) having a fluorine atom-containing group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) in which the solid content of the resin (A) is 1 to 30 parts by mass with respect to 100 parts by mass of the total of the solid contents of the resin (B) and the resin (C).

TECHNICAL FIELD

The present invention relates to a heat exchanger formed by using a heat exchange fin that is formed of an aluminum plate material formed of aluminum or an aluminum alloy, and has an excellent frost formation-suppressing effect and an excellent condensed water-removing effect imparted to a surface thereof.

BACKGROUND ART

A heat exchanger using a heat exchange fin formed of an aluminum plate material has been used in, for example, air conditioners, refrigerating equipment, and automobile equipment. In the heat exchanger for air conditioners, when the temperature of air is low or the evaporating temperature of a refrigerant is low in an outdoor unit at the time of heater operation, frost adheres onto the surface of a fin in some cases. In addition, once the frost forms, a gap between fins is clogged to increase a ventilation resistance. Eventually, the quantity of air to flow into the heat exchanger reduces and hence the evaporating ability of the heat exchanger of the outdoor unit reduces. Accordingly, when the frost adheres onto the heat exchanger, the following problem arises. The heater operation needs to be stopped and a defrosting operation needs to be performed for removing the frost, and hence comfortability remarkably reduces.

In addition, a method involving forming a hydrophobic film on the surface of the fin is available as a technology for the suppression of such frost formation. The time period during which the clogging occurs owing to the frost formation can be postponed by the method. However, after defrosting or under such a condition that the temperature of the refrigerant is relatively high so that a water droplet condenses on the surface of the fin, the method involves the following problem. Condensed water adheres to the gap between the fins, the adhering condensed water forms a bridge between the fins to increase the ventilation resistance, and as a result, heat exchange performance reduces.

Accordingly, the following has been demanded for improving the thermal efficiency of the heat exchanger at the time of the heater operation. The condensed water on the fin surface is removed before the frost formation and the fin surface is turned into a surface on which the frost formation hardly occurs. In addition, the following methods each have been proposed as means for solving the problem: a hydrophilic treatment method involving forming a hydrophilic film on the fin surface to cause the condensed water to flow down as a thin water film (Patent Literatures 1 to 3); a hydrophobic treatment method involving forming a hydrophobic film on the fin surface to remove the condensed water at an early stage (Patent Literatures 4 to 6); a hydrophobic/hydrophilic treatment method involving forming a hydrophobic film and a hydrophilic film depending on the placement and site of the fin to compensate for the disadvantages of the hydrophobic film and hydrophilic film with their advantages (Patent Literatures 7 to 9); and the like.

CITATION LIST Patent Literature

-   [PTL 1] JP 09-014888 A -   [PTL 2] JP 2000-028291 A -   [PTL 3] JP 2010-223520 A -   [PTL 4] JP 08-269367 A -   [PTL 5] JP 09-026286 A -   [PTL 6] JP 2009-270181 A -   [PTL 7] JP 08-152287 A -   [PTL 8] JP 3761262 B2 -   [PTL 9] JP 2006-046695 A

SUMMARY OF INVENTION Technical Problem

However, in the hydrophilic treatment method of each of Patent Literatures 1 to 3, a function of causing the condensed water to flow down as a thin water film is not sufficient and defrosting property by which frost formation is suppressed when performance of heater operation is not sufficient. In addition, in the hydrophobic treatment method of each of Patent Literatures 4 to 6 as well, water repellency is not sufficient and defrosting property by which the frost formation is suppressed through secure removal of a condensed water droplet is not sufficient. Further, in each of Patent Literatures 7 to 9, water-repelling performance and hydrophilic performance, in particular, the water-repelling performance in the hydrophobic film and hydrophilic film to be formed depending on the placement and site of the fin, in particular, the hydrophobic film are not necessarily sufficient. Accordingly, it is still unable to achieve a satisfactory frost formation-suppressing effect. In addition, it is still unable to sufficiently solve the problem of the increase of the ventilation resistance between the fins due to the condensed water.

Therefore, in view of the problems of the conventional technologies, the inventors of the present invention have made extensive studies to develop a heat exchanger constructed of a heat exchange fin made of an aluminum plate material that achieves compatibility between an excellent frost formation-suppressing effect exhibited by a hydrophobic film and an excellent condensed water-removing effect exhibited by a hydrophilic film to prevent frost formation, for example, at the time of heater operation, and does not cause a problem of an increase in ventilation resistance between fins due to condensed water. As a result, the inventors have found that the object can be achieved by introducing a specific crosslinked structure into the hydrophobic film, and causing the crosslinked hydrophobic film and the hydrophilic film to coexist in the same surface of the heat exchange fin, and have completed the present invention.

Therefore, an object of the present invention is to provide a heat exchanger including a heat exchange fin made of an aluminum plate material in which a crosslinked hydrophobic film and a hydrophilic film are formed on the same surface of the heat exchange fin, and compatibility between an excellent frost formation-suppressing effect exhibited by the crosslinked hydrophobic film and an excellent condensed water-removing effect exhibited by the hydrophilic film is achieved, and hence frost formation at the time of heater operation can be prevented to the extent possible, and under such a condition that condensation is liable to occur on a fin surface, a water droplet of condensed water can be quickly removed by bringing the water droplet into contact with the hydrophilic film, and as a result, a favorable heat exchange function can be continuously obtained without any increase in ventilation resistance.

Solution to Problem

That is, the present invention is a heat exchanger, including a heat exchange fin having a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy, and a crosslinked hydrophobic film having a frost formation-suppressing effect (or an anti-frost effect) and a hydrophilic film formed on a surface of the fin substrate, in which: an area occupied by the crosslinked hydrophobic film in a square area measuring 10 mm by 10 mm at an arbitrary position on a surface of the heat exchange fin is 10 to 90%; and the crosslinked hydrophobic film is formed of an aqueous hydrophobic coating composition containing a resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) in which a solid content of the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group is 1 to 30 parts by mass with respect to 100 parts by mass of a total of solid contents of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C).

The present invention is also a method of producing a heat exchanger including a heat exchange fin in which a crosslinked hydrophobic film having a frost formation-suppressing effect (or an anti-frost effect) is formed on an entirety or part of a surface of a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy, the method including: applying, to the entirety or part of the surface of the fin substrate, an aqueous hydrophobic coating composition containing a resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) in which a solid content of the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group is 1 to 30 parts by mass with respect to 100 parts by mass of a total of solid contents of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C), followed by baking of the composition to form the crosslinked hydrophobic film; and subjecting the crosslinked hydrophobic film to a post-treatment with one or two or more kinds of post-treatment liquids selected from water, an acid solution, and an alkaline solution after the formation of the crosslinked hydrophobic film.

In the present invention, the aluminum plate material forming the fin substrate may be formed of pure aluminum or may be formed of an aluminum alloy, and is not particularly limited. From the viewpoint of corrosion resistance, an anticorrosive film may be formed on each of both surfaces of the fin substrate.

The anticorrosive film to be formed on each of both surfaces of the fin substrate for the purpose is formed by applying an anticorrosive treatment agent to each of both surfaces of the fin substrate, or by performing an emmersion treatment. Examples of the anticorrosive treatment agent to be used here can include a chromate, chromate-phosphate, a chromium-free chemical conversion treatment liquid, and an organic anticorrosive primer. Of those, a chromium-free chemical conversion treatment liquid, an organic anticorrosive primer, or the like is preferred from the viewpoint of an environmentally friendly anticorrosive film.

In the present invention, the hydrophilic film is preferably formed on the entirety or part of the surface of the fin substrate, and the crosslinked hydrophobic film is preferably formed on the entirety or part of the surface of the hydrophilic film. Thus, in the heat exchange fin, the crosslinked hydrophobic film is preferably formed on part of its surface in a nonuniform and spotted manner, or the crosslinked hydrophobic film and the hydrophilic film desirably cooperate with each other to form a sea-island structure in which the cross-linked hydrophobic film forms a sea portion and the hydrophilic film forms an island portion. When the crosslinked hydrophobic film having a frost formation-suppressing effect and the hydrophilic film are formed on the surface of the fin substrate as described above, frost formation at the time of heater operation can be prevented to the extent possible by an excellent frost formation-suppressing effect and frost formation suppression-maintaining effect exhibited by the crosslinked hydrophobic film, and under such a condition that condensation is liable to occur on a fin surface, a water droplet of produced condensed water can be quickly removed by bringing the water droplet into contact with the hydrophilic film by virtue of the condensed water-removing effect of the hydrophilic film.

Here, a method of forming the crosslinked hydrophobic film having a frost formation-suppressing effect on the entirety or part of the surface of the fin substrate, preferably the entirety or part of the surface of the hydrophilic film formed on the surface of the fin substrate is not particularly limited. For example, as a method of forming the crosslinked hydrophobic film on the same surface as a spot pattern, there are given a method involving adding a silicone-based hydrophobic agent to a hydrophobic coating material and splashing part of the mixture at the time of the formation of the cross-linked hydrophobic film to provide a spot pattern, a method involving painting the surface with the hydrophobic coating material in a thin-film manner through the use of a spray upon its application to form a painted portion and an unpainted portion, a method involving forming irregular portions on the surface of the fin substrate (roughened surface) or the surface of the hydrophilic film (coating film surface) on which the crosslinked hydrophobic film is to be formed, forming the crosslinked hydrophobic film in a recessed portion of the irregular portions, and controlling the thickness of the crosslinked hydrophobic film to cause the head of a protruded portion of the irregular portions to appear from the crosslinked hydrophobic film, and a method involving painting the surface of the fin substrate (roughened surface) or the surface of the hydrophilic film (coating film surface) on which the crosslinked hydrophobic film is to be formed with a water-soluble resin or the like so that a spot pattern may be obtained, then painting the painted surface with the hydrophobic coating material, and then performing water washing, acid washing, or alkali washing to remove the crosslinked hydrophobic film formed on the water-soluble resin to form the crosslinked hydrophobic film into a spot pattern.

In the present invention, after the crosslinked hydrophobic film having a frost formation-suppressing effect has been formed on the entirety or part of the surface of the fin substrate, the crosslinked hydrophobic film is subjected to a post-treatment with water, an acid solution, or an alkaline solution, and hence hydrophilicity can be expressed, the frost formation at the time of the heater operation can be prevented to the extent possible by an excellent frost formation-suppressing effect and frost formation suppression-maintaining effect, and under such a condition that condensation is liable to occur on the fin surface, a water droplet of condensed water easily flows and the water droplet can be quickly removed.

Although the post-treatment with water for the expression of the hydrophilicity is not particularly limited, the heat exchange fin after the formation of the crosslinked hydrophobic film is subjected to water washing with, for example, tap water, industrial water, or ion-exchanged water through immersion or spraying under the conditions of preferably normal temperature to 100° C. and 5 sec to 3 hr, more preferably 40 to 100° C. and 10 sec to 1 hr. In addition, although the post-treatment with the acid solution for the expression of the hydrophilicity is not particularly limited, the heat exchange fin after the formation of the crosslinked hydrophobic film is subjected to washing through immersion or spraying under the conditions of preferably normal temperature to 100° C. and 5 sec to 3 hr, more preferably 40 to 100° C. and 10 sec to 1 hr. Although the acid solution is not particularly limited, an aqueous solution of an inorganic acid such as sulfuric acid, nitric acid, phosphoric acid, or boric acid, or an organic acid such as acetic acid, citric acid, or oxalic acid is used. In addition, although the post-treatment with the alkaline solution for the expression of the hydrophilicity is not particularly limited, the heat exchange fin after the formation of the crosslinked hydrophobic film is subjected to washing through immersion or spraying under the conditions of preferably normal temperature to 100° C. and 5 sec to 3 hr, more preferably 40° C. to 100° C. and 10 sec to 1 hr. Although the alkaline solution is not particularly limited, an aqueous solution of, for example, sodium hydroxide, sodium hydrogen carbonate, or sodium silicate is permitted. It should be noted that after the washing with the acid solution or the alkaline solution, water washing may be performed after neutralization with the alkaline solution or the acid solution.

Here, the water contact angle of the crosslinked hydrophobic film having a frost formation-suppressing effect is preferably 100° or more, more preferably 105° or more, and its thickness is typically 0.05 to 5.0 μm, preferably 0.1 to 4.0 μm, more preferably 0.2 to 2.0 μm. The water contact angle of the crosslinked hydrophobic film is desirably as large as possible.

However, when the water contact angle of the crosslinked hydrophobic film is less than 100°, there arises a problem in that the frost formation-suppressing effect reduces. In addition, when the thickness of the crosslinked hydrophobic film is less than 0.05 μm, for example, the following problem arises. Variations in frost formation suppression and hydrophilicity between lots enlarge, and the deterioration of the frost formation suppression and hydrophilicity-maintaining property over time enlarges. In contrast, when the thickness exceeds 5.0 μm, neither additional frost formation suppression nor an additional improvement in hydrophilicity can be expected. In addition, for example, the following problem arises. The burn of the film due to heat upon brazing of a copper tube for a refrigerant to the fin material becomes rather conspicuous and a cost increases with increasing thickness.

In the present invention, the crosslinked hydrophobic film that exhibits a frost formation-suppressing effect is formed by applying the aqueous hydrophobic coating composition, and as the aqueous hydrophobic coating composition to be used for the purpose, there can be given an aqueous hydrophobic coating composition containing the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, the quaternary ammonium salt group-containing modified epoxy resin (B), and the amino resin (C) from the viewpoint of long-term maintenance of frost formation suppression. It should be noted that in the following description, the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group is sometimes referred to as “resin (A) having a fluorine atom-containing group.”

<Resin (A) Having Fluorine Atom-Containing Group>

In the aqueous hydrophobic coating material, a known resin can be used as the resin (A) having a fluorine atom-containing group as long as the resin has a perfluoroalkyl group and/or a perfluoroalkenyl group, and a resin dispersed or dissolved in water or a medium using water as a main component (hereinafter referred to as “aqueous medium”) can be used. Such resin (A) having a fluorine atom-containing group is preferably, for example, a resin obtained by subjecting a polymerizable unsaturated monomer (a-1) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group (hereinafter sometimes described as the “polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group”) of a structure represented by the following general formula (I) and any other polymerizable unsaturated monomer (a-2) to a copolymerization reaction. A method of performing the polymerization reaction can be selected from known polymerization methods, and examples thereof can include bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, and dispersion polymerization. Of those, emulsion polymerization is preferred from the viewpoint of, for example, the efficiency with which the resin dispersed or dissolved in the aqueous medium is produced.

(In the formula, Rf represents a linear or branched perfluoroalkyl group or perfluoroalkenyl group having 1 to 21 carbon atoms. R represents a hydrogen atom, a halogen atom, or a methyl group. X represents an oxygen atom or an imino group. Y represents a divalent organic group having 1 to 20 carbon atoms that may contain an oxygen atom, a sulfur atom, a nitrogen atom, or a phosphorus atom.)

The fluorine atom-containing group is preferably a perfluoroalkyl group, and examples of the perfluoroalkyl group include —CF₃, —CF₂CF₃, —CF₂CF₂CF₃, —CF(CF₃)₂, —CF₂CF₂CF₂CF₃, —CF₂CF(CF₃)₂, —C(CF₃)₃, —(CF₂)₄CF₃, —(CF₂)₂CF (CF₃)₂, —CF₂C(CF₃)₃, —CF(CF₃)CF₂CF₂CF₃, —(CF₂)₅CF₃, —(CF₂)₃CF (CF₃)₂, —(CF₂)₄CF (CF₃)₂, —(CF₂)₇CF₃, —(CF₂)₅CF(CF₃)₂, —(CF₂)₆CF(CF₃)₂, and —(CF₂)₉CF₃. The perfluoroalkyl group has 1 to 21 carbon atoms, preferably 2 to 20 carbon atoms, more preferably 4 to 16 carbon atoms.

The emulsion polymerization of the polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group can be performed by a known method involving subjecting a mixture of the monomer (a-1) and the other polymerizable unsaturated monomer (a-2) to emulsion polymerization with an emulsifier and a polymerization initiator in the aqueous medium. It should be noted that in the emulsion polymerization, a hydrophilic or hydrophobic organic solvent may be used as required.

A conventionally known emulsifier can be used as the emulsifier, and examples thereof include an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a combination thereof. A compound having a fluorine atom of, for example, a fluorinated alkyl group bonded thereto may be used as the surfactant as required.

A conventionally known polymerization initiator can be used as the polymerization initiator, and examples thereof include: persulfates such as ammoniumpersulfate (APS), potassiumpersulfate, and sodium persulfate; and oil-soluble polymerization initiators such as diisopropyl peroxydicarbonate (IPP), benzoyl peroxide, dibutyl peroxide, and azobisisobutyronitrile (AIBN).

In addition, a chain transfer agent may be used in the emulsion polymerization reaction, and examples of the chain transfer agent include: malonic acid diesters such as diethyl malonate (MDE) and dimethyl malonate; acetic acid esters such as ethyl acetate and butyl acetate; alcohols such as methanol and ethanol; mercaptans such as n-lauryl mercaptan and n-octyl mercaptan; and an α-methylstyrene dimer.

An aqueous dispersion of the resin (A) having a fluorine atom-containing group can be produced by performing the polymerization reaction at a polymerization temperature of 20 to 150° C. for a polymerization time of 0.1 to 100 hr. In the aqueous dispersion, the resin (A) having a fluorine atom-containing group is obtained as particles having an average particle diameter of 10 to 500 nm, preferably 30 to 200 nm. Its solid content concentration is desirably about 5 to 50 mass %.

Each of the particles of the resin (A) having a fluorine atom-containing group may be of a monolayer structure or may be of a multilayer structure including a core-shell structure. In addition, the inside of each of the particles may be crosslinked and those particles can be obtained by a known method in emulsion polymerization.

A monomer having copolymerization reactivity to the polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group can be used as the other polymerizable unsaturated monomer (a-2) without any particular limitation. Examples thereof can include: acrylic acid; methacrylic acid; itaconic acid; itaconic anhydride; maleic anhydride; butadiene; isoprene; chloroprene; a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms; a (meth)acrylic acid cyclohexyl ester; isobornyl (meth)acrylate; a (meth)acrylic acid benzyl ester; polyethylene glycol di(meth)acrylate; aromatic vinyl-based monomers such as styrene, α-methylstyrene, and p-methylstyrene; hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyamyl (meth)acrylate, and hydroxyhexyl (meth)acrylate; a vinyl alkyl ether in which the alkyl group has 1 to 20 carbon atoms; a halogenated alkyl vinyl ether in which the alkyl group has 1 to 20 carbon atoms; a vinyl alkyl ketone in which the alkyl group has 1 to 20 carbon atoms; silyl group-containing unsaturated monomers such as vinyltriethoxysilane and γ-(methacryloxypropyl)trimethoxysilane; (meth)acrylamide-based monomers such as (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, N-n-propoxymethyl (meth)acrylamide, N-isopropoxymethyl (meth)acrylamide, N-n-butoxymethyl (meth)acrylamide, N-sec-butoxymethyl (meth)acrylamide, and N-tert-butoxymethyl (meth)acrylamide; vinyl esters such as vinyl acetate and “VeoVa” (vinyl ester manufactured by Shell); acrylonitrile; methacrylonitrile ethylene; and butadiene. It should be noted that herein, the term “(meth)acrylic acid” is a collective term for acrylic acid and methacrylic acid, the term “(meth)acrylate” is a collective term for acrylate and methacrylate, and the term “(meth)acrylamide” is a collective term for acrylamide and methacrylamide.

A commercial product of the resin (A) having a fluorine atom-containing group dissolved or dispersed in an aqueous medium is, for example, UNIDYNE TG-652, UNIDYNE TG-664, UNIDYNE TG-410, UNIDYNE TG-5521 UNIDYNE TG-5601, UNIDYNE TG-8711, UNIDYNE TG-470B, UNIDYNE TG-500S, UNIDYNE TG-580, UNIDYNE TG-581, or UNIDYNE TG-658 (all of which are manufactured by DAIKIN, trade name), SWK-601 (manufactured by SEIMI CHEMICAL), FS6810 (manufactured by Fluoro Technology), or NK GUARD SR-108 (manufactured by NICCA CHEMICAL CO., LTD).

Instead of the method based on the copolymerization reaction between the polymerizable unsaturated monomer (a-1) having a fluorine atom-containing group and the other polymerizable unsaturated monomer (a-2), the production of the resin (A) having a fluorine atom-containing group can be similarly performed by a polymerization reaction between the polymerizable unsaturated monomers involving using a perfluoroalkyl group-containing radical generator as a polymerization initiator, and examples of the polymerization initiator can include fluorine-containing organic peroxides described in JP 2010-195937 A.

<Quaternary Ammonium Salt Group-Containing Modified Epoxy Resin (B)>

The aqueous hydrophobic coating material contains the quaternary ammonium salt group-containing modified epoxy resin (B) to be described below from the viewpoints of the processability, adhesiveness, moisture resistance, and corrosion resistance of a coating film to be obtained.

The modified epoxy resin (B) can be produced by subjecting a mixture containing an epoxy resin (b-1), a carboxyl group-containing acrylic resin (b-2), and an amine compound (b-3) to a reaction. In the reaction, a reaction for producing a quaternary ammonium salt group, and an esterification reaction between an epoxy group in the epoxy resin and a carboxyl group in the carboxyl group-containing acrylic resin progress to produce the quaternary ammonium salt group-containing modified epoxy resin (B). In addition, in the reaction, the epoxy group of the epoxy resin (b-1) opens to produce a hydroxyl group. Thus, the quaternary ammonium salt group-containing modified epoxy resin (B) has a hydroxyl group, which is reactive with the amino resin (C) to be described later.

A bisphenol-type epoxy resin is preferred as the epoxy resin (b-1) from the viewpoints of adhesiveness and corrosion resistance. The bisphenol-type epoxy resin is a resin obtained by a reaction between a bisphenol compound and an epihalohydrin such as epichlorhydrin.

Examples of the bisphenol compound can include bis(4-hydroxyphenyl)-2,2-propane (bisphenol A), 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)methane (bisphenol F), and 4,4-dihydroxydiphenyl sulfone (bisphenol S). Of those bisphenol-type epoxy resins (b-1), a bisphenol A-type epoxy resin is preferably used from the viewpoint of corrosion resistance.

From the viewpoints of, for example, the dispersion stability in an aqueous medium and the processability and hygiene of the coating film to be obtained, it is suitable to use the bisphenol-type epoxy resin (b-1) having a number-average molecular weight in the range of 4,000 to 30,000, preferably 5,000 to 30,000, and having an epoxy equivalent of 2,000 to 10,000, preferably 2,500 to 10,000.

As a commercial product of a bisphenol A-type epoxy resin that can be used as the bisphenol-type epoxy resin (b-1), there can be given, for example, jER1010, jER1256B40, and jER1256 manufactured by Japan Epoxy Resins Co. Ltd.

In addition, the bisphenol A-type epoxy resin may be a bisphenol A-type modified epoxy resin obtained by modifying a bisphenol A-type epoxy resin with a dibasic acid. In this case, a resin having a number-average molecular weight in the range of 2,000 to 8,000 and an epoxy equivalent in the range of 1,000 to 4,000 can be suitably used as the bisphenol A-type epoxy resin to be caused to react with the dibasic acid. In addition, a compound represented by a general formula “HOOC—(CH₂)_(n)—COOH (where n represents an integer of 1 to 12),” specifically, for example, succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecanedioic acid, or hexahydrophthalic acid can be used as the dibasic acid, and adipic acid can be particularly suitably used.

The bisphenolA-type modified epoxy resin can be obtained by subjecting a mixture of the bisphenol A-type epoxy resin and the dibasic acid to a reaction in the presence of an esterification catalyst such as tri-n-butylamine and an organic solvent at a reaction temperature of 120 to 180° C. for a reaction time of about 1 to 4 hr.

The carboxyl group-containing acrylic resin (b-2) to be used in the production of the quaternary ammonium salt group-containing modified epoxy resin (B) can be produced by subjecting a mixture containing a carboxyl group-containing polymerizable unsaturated monomer and any other polymerizable unsaturated monomer to a copolymerization reaction with, for example, a radical polymerization initiator through heating in an organic solvent at 80 to 150° C. for 1 to 10 hr.

As the other polymerizable unsaturated monomer that can be used in the production of the carboxyl group-containing acrylic resin (b-2), there can be given the other polymerizable unsaturated monomer (a-2) described for the resin (A) having a fluorine atom-containing group.

As the polymerization initiator, for example, an organic peroxide-based or azo-based polymerization initiator is used. Examples of the organic peroxide-based polymerization initiator include benzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, di-t-butyl peroxide, t-butyl peroxybenzoate, and t-amyl peroxy-2-ethylhexanoate, and examples of the azo-based polymerization initiator include azobisisobutyronitrile and azobisdimethylvaleronitrile.

In the copolymerization reaction, a chain transfer agent may be used, and examples thereof include known agents such as an α-methylstyrene dimer and a mercaptan compound.

The carboxyl group-containing acrylic resin (b-2) has a weight-average molecular weight in the range of preferably 5,000 to 100,000, more preferably 10,000 to 100,000 and a resin acid value in the range of preferably 150 to 700 mgKOH/g, more preferably 200 to 500 mgKOH/g from the viewpoints of its stability in an aqueous medium, and the processability and adhesiveness of the coating film to be obtained.

The amine compound (b-3) is preferably a tertiary amine compound such as triethylamine, dimethylethanolamine, triethanolamine, monomethyldiethanolamine, or N-methylmorpholine.

The quaternary ammonium salt group-containing modified epoxy resin (B) can be produced by subjecting the mixture containing the epoxy resin (b-1), the carboxyl group-containing acrylic resin (b-2), and the amine compound (b-3) to a reaction through heating in an organic solvent at 80 to 120° C. for 0.5 to 8 hr.

A blending ratio between the epoxy resin (b-1) and the carboxyl group-containing acrylic resin (b-2) in the reaction, which has only to be appropriately selected depending on painting workability and coating film performance, falls within the range of preferably 10/90 to 95/5, more preferably 60/40 to 90/10 in terms of a solid content mass ratio “resin (b-1)/resin (b-2).”

The usage of the amine compound (b-3) suitably falls within the range of 1 to 10 mass % with reference to the total solid content of the epoxy resin (b-1) and the carboxyl group-containing acrylic resin (b-2) from the viewpoints of the moisture resistance and corrosion resistance of the resultant film.

The quaternary ammonium salt group-containing modified epoxy resin (B) obtained by the reaction has an acid value in the range of preferably 20 to 120 mgKOH/g, more preferably 30 to 100 mgKOH/g and a weight-average molecular weight in the range of preferably 1,000 to 40,000, more preferably 2,000 to 15,000 from the viewpoints of its stability in an aqueous medium, and the processability, adhesiveness, moisture resistance, and corrosion resistance of the coating film to be obtained.

It should be noted that the weight-average molecular weight in the description is a value obtained by converting a retention time (retention volume) measured with tetrahydrofuran as a solvent by gel permeation chromatography with reference to the weight-average molecular weight of a polystyrene. In addition, the number-average molecular weight is a value determined from the weight-average molecular weight by calculation.

“HLC8120GPC” (manufactured by Tosoh Corporation) was used as a gel permeation chromatograph. Four columns, i.e., “TSKgel G-4000HXL,” “TSKgel G-3000HXL,” “TSKgel G-2500HXL,” and “TSKgel G-2000HXL” (all of which were manufactured by Tosoh Corporation, trade name) were used, and the measurement was performed under the following conditions: mobile phase; tetrahydrofuran, measurement temperature; 40° C., flow rate; 1 ml/min, and detector; RI.

The quanternary ammonium salt group-containing modified epoxy resin (B) is neutralized and dispersed in an aqueous medium, and a basic compound such as an amine or ammonia is suitably used as a neutralizer to be used in the neutralization.

Typical examples of the amine include triethylamine, triethanolamine, dimethylethanolamine, diethylethanolamine, and morpholine. Of those, triethylamine and dimethylethanolamine are particularly suitable. For the neutralization of the quanternary ammonium salt group-containing modified epoxy resin (B), it is generally preferred that the neutralization be performed in the range of 0.2 to 2.0 equivalents with respect to carboxyl groups in the resin.

In the present invention, the amount of a quaternary ammonium salt group formed at the time of the esterification reaction and by the neutralization (the number of moles of the quaternary ammonium salt group contained per 1 g of the resin) preferably falls within the range of 3.0×10⁻⁴ mol/g or less, preferably within the range of 0.6×10⁻⁴ to 3.0×10⁻⁴ mol/g, more preferably within the range of 0.8×10⁻⁴ to 2.5×10⁻⁴ mol/g from the viewpoints of the adhesiveness, the moisture resistance, and the corrosion resistance.

Here, the measurement of the quaternary ammonium salt group amount is performed as described below. A titration reaction is performed by dropping, to a sample solution obtained by dissolving a sample after the initiation of the reaction in a solvent, an indicator solution obtained by dissolving an indicator having a sulfonic group and a hydroxyl group as functional groups in a solvent. For each of the first stage of the titration reaction where the indicator and a quaternary ammonium salt of an epoxy compound react with each other to form an indicator in which both a sulfonic group and a hydroxyl group have been simultaneously ionized, and a carboxylic acid, and the second stage of the titration reaction where the indicator and the ionized indicator react with each other to form an indicator in which only a sulfonic group has been ionized, a relationship between a titer and an electric conductivity is plotted. A titer t₁ in the first stage is determined from a titer at the point of intersection between a straight line connecting the plots in the first stage and a straight line connecting the plots in the second stage, and then the amount (mol/g) of the quaternary ammonium salt in 1 g of the sample in terms of a solid content is determined from the following equation (1).

Quaternary ammonium salt amount (mol/g)=t ₁ (ml)×2×indicator concentration (mol/l)×(1/1,000)×{100/(sample (g)×solid content (%))}  Equation (1)

It should be noted that an aqueous medium in which the quaternary ammonium salt group-containing modified epoxy resin (B) is dispersed may be water alone or may be a mixture of water and an organic solvent. Any one of the conventionally known solvents can be used as the organic solvent as long as the stability of the quaternary ammonium salt group-containing modified epoxy resin (B) in the aqueous medium is not impaired.

<Amino Resin (C)>

Examples of the amino resin (C) in the aqueous hydrophobic coating material include a melamine resin, a urea resin, and a benzoguanamine resin. Of those, a melamine resin is preferred from the viewpoints of the processability and the adhesiveness.

Examples of the melamine resin include a partially etherified or fully etherified melamine resin obtained by etherifying part or all of the methylol groups of methylolated melamine with a monohydric alcohol having 1 to 8 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, or 2-ethylhexanol.

As such resin, there can be used one in which the methylol groups are fully etherified or one in which the methylol groups are partially etherified and methylol groups and imino groups remain. Examples thereof can include alkyl-etherified melamines such as methyl-etherified melamine, ethyl-etherified melamine, and butyl-etherified melamine. One kind of these malamines may be used alone, or two or more kinds thereof may be used in combination as required. Of those, a methyl-etherified melamine resin in which at least part of the methylol groups are methyl-etherified is suitable.

Commercial products of the melamine resin satisfying such conditions are commercially available under, for example, the following trade names: “CYMEL 202,” “CYMEL 232,” “CYMEL 235,” “CYMEL 238,” “CYMEL 254,” “CYMEL 266,” “CYMEL 267,” “CYMEL 272,” “CYMEL 285,” “CYMEL 301,” “CYMEL 303,” “CYMEL 325,” “CYMEL 327,” “CYMEL 350,” “CYMEL 370,” “CYMEL 701,” “CYMEL 703,” “CYMEL 736,” “CYMEL 738,” “CYMEL 771,” “CYMEL 1141,” “CYMEL 1156,” “CYMEL 1158,” “MYCOAT 212,” “MYCOAT 715,” and “MYCOAT 776” (all of which are manufactured by Nihon Cytec Industries Inc.); “U-VAN 120,” “U-VAN 20HS,” “U-VAN 2021,” “U-VAN 2028,” and “U-VAN 2061” (all of which are manufactured by Mitsui Chemicals, Inc.); and “Melan 522” (manufactured by Hitachi Chemical Co., Ltd.).

It should be noted that a blending ratio between the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C) falls within the range of preferably 95/5 to 50/50, particularly preferably 93/7 to 60/40 in terms of a solid content mass ratio “quaternary ammonium salt group-containing modified epoxy resin (B)/amino resin (C).” When the amount of the amino resin (C) is excessively small, sufficient curability is not obtained. When the amount is excessively large, the processability of an aluminum fin material may reduce.

The content of the resin (A) having a fluorine atom-containing group in the aqueous hydrophobic coating composition is 1 to 30 parts by mass, preferably 3 to 25 parts by mass, more preferably 10 to 22 parts by mass in terms of a solid content with respect to 100 parts by mass of the total of the solid contents of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C) from the viewpoints of frost formation suppression, the corrosion resistance, and coating stability.

It should be noted that additives such as a basic compound, a crosslinking agent other than the amino resin (C) (such as a blocked polyisocyanate), colloidal silica, an antibacterial agent, a coloring pigment, a rust preventive pigment known per se (such as a chromate-based, lead-based, or molybdic acid-based pigment), and a rust preventive agent (such as: a phenolic carboxylic acid, e.g., tannic acid or gallic acid and a salt thereof; an organic phosphoric acid, e.g., phytic acid or phosphinic acid; a metal biphosphate; or a nitrite), and an aqueous medium can be added to the aqueous hydrophobic coating composition in the present invention in addition to the resin (A) having a fluorine atom-containing group, the quanternary ammonium salt group-containing modified epoxy resin (B), and the amino resin (C) as required.

The aqueous medium may be water or may be a mixed solvent of water and a small amount of an organic solvent or any one of the basic compounds such as amines and ammonia. The content of water in the mixed solvent is typically 80 mass % or more.

In addition, in the present invention, the hydrophilic film exhibiting a condensed water-removing effect may be formed by applying a hydrophilic coating material. Examples of the hydrophilic coating material to be used for the purpose can include: inorganic coating materials such as water glass-based, silica-based, and boehmite-based coating materials; an organic hydrophilic coating material containing a water-soluble acrylic resin, a water-soluble cellulose resin, a water-soluble amino resin, a polyvinyl alcohol, or the like; and an organic-inorganic composite hydrophilic coating material containing an inorganic material and an organic resin.

A known coating material can be used as the organic hydrophilic coating material and examples thereof can include the following organic hydrophilic coating compositions (E):

(1) an organic hydrophilic coating material containing a polyvinyl alcohol having a saponification degree of 87% or more and a neutralized resin obtained by the formation of a salt of at least part of the carboxyl groups of a high-acid value acrylic resin having a resin acid value of 300 mgKOH/g or more with a basic compound that does not have a boiling point of less than 180° C. and does not decompose at less than 180° C.; and

(2) an organic hydrophilic coating material containing a polyvinyl alcohol-based resin and a polyethylene glycol-based resin as main components, and containing a nitric acid compound having a monovalent or divalent element (see JP 2002-275407 A).

In addition, in the present invention, the hydrophilic film exhibiting a condensed water-removing effect may be formed by applying a flux to be used in the step of brazing the fin. Examples of the flux can include fluoride-based fluxes such as KAlF₄, K₂AlF₅.H₂O, a complex compound of KAlF₄ and K₃AlF₆, KZnF₃, K₂SiF₆, Li₃AlF₆, and CsAlF₄. One kind or more of those fluxes are used as a mixture.

The application of the hydrophobic coating material, the hydrophilic coating material, or the flux is performed by applying means such as a roll coating method, a bar coating method, a spraying method, an immersion method, or a spin coating method, and is performed by a method involving using a precoated fin material obtained by painting an aluminum material through the use of a roll coater or the like, or a post-coating method involving applying such coating material or flux to a heat exchanger constructed of an aluminum fin material through spraying or immersion. At this time, the hydrophobic coating material or the hydrophilic coating material is appropriately diluted so as to have a predetermined concentration before use.

In addition, the water contact angle of the hydrophilic film is preferably 40° or less, more preferably 30° or less, and its thickness is typically 0.1 to 200 μm, preferably 0.2 to 100 μm, more preferably 0.5 to 100 μm. In addition, when the hydrophilic film is a film formed in the brazing step, its water contact angle is preferably 40° or less, more preferably 30° or less, and its thickness is typically 0.1 to 200 μm or less, preferably 1 to 100 μm, more preferably 5 to 100 μm.

The water contact angle of the hydrophilic film is desirably as small as possible. However, when the water contact angle of the hydrophilic film is more than 40°, a problem in that condensed water hardly flows arises. In addition, when the thickness of the hydrophilic film is less than 0.1 μm, as in the case of the crosslinked hydrophobic film, for example, the following problem arises. Variations in frost formation suppression and hydrophilicity between lots enlarge, and the deterioration of the frost formation suppression and hydrophilicity-maintaining property over time enlarges. In contrast, when the thickness exceeds 200 μm, neither additional frost formation suppression nor an additional improvement in hydrophilicity can be expected. In addition, for example, the following problem arises. A cost increases with increasing thickness.

<Method of Forming Films for Heat Exchanger Fin>

(1) Case of Precoated Fin

A method of applying the anticorrosive film, the crosslinked hydrophobic film, and the hydrophilic film on the surfaces of various hard materials is not particularly limited. For example, in the case of a precoated fin, a method involving using a generally used roll coater, a bar coating method, or a spray method can be adopted.

For example, when the crosslinked hydrophobic film is formed on the surface of the fin substrate made of an aluminum plate material for heat exchangers with the aqueous hydrophobic coating composition, first, the aqueous hydrophobic coating composition is applied to the aluminum material with a roller coater or the like, and then the resultant is subjected to heating with, for example, a floater oven under high-temperature ventilation, preferably heating under a high-temperature ventilation of 10 to 30 m/min at a high temperature of 60 to 300° C. for 2 sec to 30 min.

In addition, when the crosslinked hydrophobic film is formed after the formation of the hydrophilic film, the hydrophilic treatment agent is applied to the surface of the fin substrate made of an aluminum plate material for heat exchangers, then the resultant is subjected to heating with, for example, a floater oven under high-temperature ventilation, preferably heating under a high-temperature ventilation of 10 to 30 m/min at a high temperature of 60 to 300° C. for 2 sec to 30 min, then the aqueous hydrophobic coating composition is applied to the heated product, and then the resultant is subjected to heating with, for example, a floater oven under high-temperature ventilation, preferably heating under a high-temperature ventilation of 10 to 30 m/min at a high temperature of 60 to 300° C. for 2 sec to 30 min.

(2) Case of Post-Coating Painting

With regard to a method of applying the anticorrosive film, the crosslinked hydrophobic film, and the hydrophilic film to various surfaces, in the heat exchanger using an aluminum fin material, the hydrophilic film, the anticorrosive film, and the crosslinked hydrophobic film are formed by post-coating.

When the heat exchanger using the heat exchange fin made of an aluminum plate material is formed of, for example, a heat exchanger obtained by brazing a flat flow channel tube and a corrugated fin, the hydrophilic film and the crosslinked hydrophobic film, or the hydrophilic film, the anticorrosive film, and the crosslinked hydrophobic film are formed in the heat exchanger obtained by brazing the flat flow channel tube and the corrugated fin by post-coating. In this case, the hydrophilic film is formed by applying a flux to be used at the time of the brazing by a spraying method, an immersion method, or the like, and the anticorrosive film and the crosslinked hydrophobic film are each formed by treating and applying the anticorrosive treatment liquid or the aqueous hydrophobic coating material by the immersion method, the spraying method, or the like, and then heating the liquid or coating material at 60 to 300° C. for 2 sec to 30 min.

For example, when the flat flow channel tube and the corrugated fin are brazed with a fluoride-based flux, the following may be adopted. A flux slurry is applied with a shower, a spray, a brush, or the like and dried, and is then heated at 590 to 610° C. for 3 to 10 min to form an inorganic hydrophilic film on the flat flow channel tube and/or the corrugated fin. After the film has been cooled, post-coating with the aqueous hydrophobic coating material is performed by the method.

Alternatively, the following may be adopted. The flux is applied to perform brazing so that an inorganic hydrophilic film may be formed on the flat flow channel tube and/or the corrugated fin. After the film has been cooled, post-coating with the anticorrosive coating material is performed by the method and then post-coating with the aqueous hydrophobic coating material is performed by the method.

In the heat exchange fin of the present invention, a ratio between the crosslinked hydrophobic film and hydrophilic film formed on its surface needs to be as described below. An area occupied by the crosslinked hydrophobic film in a square area measuring 10 mm by 10 mm at an arbitrary position on the surface of the heat exchange fin is 10 to 90%, preferably 20 to 80%. When the area occupied by the crosslinked hydrophobic film is less than 10%, a problem in that the frost formation-suppressing effect becomes insufficient arises. In contrast, when the area is more than 90%, a problem in that the condensed water-removing effect becomes insufficient arises.

Advantageous Effects of Invention

According to the heat exchanger of the present invention, the crosslinked hydrophobic film and the hydrophilic film are formed on the same surface of the heat exchange fin made of an aluminum plate material, and an excellent frost formation-suppressing effect exhibited by the crosslinked hydrophobic film and an excellent condensed water-removing effect exhibited by the hydrophilic film cooperate with each other, and hence frost formation at the time of heater operation can be prevented to the extent possible, and under such a condition that condensation is liable to occur on a fin surface, a water droplet of condensed water can be quickly removed by bringing the water droplet into contact with the hydrophilic film, and as a result, a favorable heat exchange function can be maintained without any increase in ventilation resistance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective explanatory diagram illustrating a heat exchanger made of an aluminum alloy obtained in each of Examples 5 to 12 and Comparative Examples 1 to 8.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferred embodiment of the present invention is specifically described on the basis of examples and comparative examples.

Production Example of Aqueous Hydrophobic Coating Composition

In the following production examples, the term “part (s)” refers to “part (s) by mass” and the term “%” refers to “mass %.”

(1) Production of Carboxyl Group-Containing Acrylic Resin (Ca) to be Used in Production of Ammonium Salt Group-Containing Modified Epoxy Resin (B) Production Example 1 Solution of Carboxyl Group-Containing Acrylic Resin (ca-1)

850 parts of n-butanol were heated to 100° C. in a stream of nitrogen, and then a monomer mixture and a polymerization initiator “450 parts of methacrylic acid, 450 parts of styrene, 100 parts of ethyl acrylate, and 40 parts of t-butyl peroxy-2-ethylhexanoate” were dropped therein over 3 hr. After the dropping, the resultant mixture was aged for 1 hr. Next, a mixed solution of 10 parts of t-butyl peroxy-2-ethylhexanoate and 100 parts of n-butanol was dropped to the aged product over 30 min, and after the dropping, the resultant mixture was aged for 2 hr. Next, 933 parts of n-butanol and 400 parts of ethylene glycol monobutyl ether were added to the aged product to provide a solution of a carboxyl group-containing acrylic resin (ca-1) having a solid content of about 30%. The resultant resin had a resin acid value of 300 mgKOH/g and a weight-average molecular weight of about 17,000.

Production Example 2 Solution of Carboxyl Group-Containing Acrylic Resin (Ca-2)

1,400 parts of n-butanol were heated to 100° C. in a stream of nitrogen, and then a monomer mixture and a polymerization initiator “670 parts of methacrylic acid, 250 parts of styrene, 80 parts of ethyl acrylate, and 50 parts of t-butyl peroxy-2-ethylhexanoate” were dropped therein over 3 hr. After the dropping, the resultant mixture was aged for 1 hr. Next, a mixed solution of 10 parts of t-butyl peroxy-2-ethylhexanoate and 100 parts of n-butanol was dropped to the aged product over 30 min, and after the dropping, the resultant mixture was aged for 2 hr. Next, 373 parts of n-butanol and 400 parts of ethylene glycol monobutyl ether were added to the aged product to provide a solution of a carboxyl group-containing acrylic resin (ca-2) having a solid content of about 30%. The resultant resin had a resin acid value of 450 mgKOH/g and a weight-average molecular weight of about 14,000.

(2) Production of Ammonium Salt Group-Containing Modified Epoxy Resin (ae) Production Example 3 Aqueous Dispersion of Ammonium Salt Group-Containing Modified Epoxy Resin (ae-1)

513 parts of a jER828EL (manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent: about 190, number-average molecular weight: about 380), 287 parts of bisphenol A, 0.3 part of tetramethylammonium chloride, and 89 parts of methyl isobutyl ketone were loaded, and were then subjected to a reaction for about 4 hr while being heated to 140° C. in a stream of nitrogen. Thus, an epoxy resin solution was obtained. The resultant epoxy resin had an epoxy equivalent of 3,700 and a number-average molecular weight of about 17,000.

Next, 667 parts of the solution of the carboxyl group-containing acrylic resin (ca-1) having a solid content of about 30% obtained in Production Example 1 were charged into the resultant epoxy resin solution, and were then uniformly dissolved by heating to 90° C. After that, 40 parts of deionized water were dropped to the solution at the temperature over 30 min. Next, 30 parts of dimethylethanolamine were added to the mixture and then the whole was subjected to a reaction by being stirred for 1 hr. Further, 2,380 parts of deionized water were added to the resultant over 1 hr to provide an aqueous dispersion of an ammonium salt group-containing modified epoxy resin (ae-1) having a solid content of about 25%. The resultant resin had a resin acid value of 48 mgKOH/g, a quaternary ammonium salt amount (based on the electric conductivity titration method in the description) of 1.2×10⁻⁴ mol/g, and a weight-average molecular weight of 26,000.

Production Example 4 Aqueous Dispersion of Ammonium Salt Group-Containing Modified Epoxy Resin (ae-2)

519 parts of a jER828EL (manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent: about 190, number-average molecular weight: about 380), 281 parts of bisphenol A, 0.3 part of tetramethylammonium chloride, and 89 parts of methyl isobutyl ketone were loaded, and were then subjected to a reaction for about 4 hr while being heated to 140° C. in a stream of nitrogen. Thus, an epoxy resin solution was obtained. The resultant epoxy resin had an epoxy equivalent of 2,800 and a number-average molecular weight of about 12,000.

Next, 667 parts of the solution of the carboxyl group-containing acrylic resin (ca-2) having a solid content of about 30% obtained in Production Example 2 were charged into the resultant epoxy resin solution, and were then uniformly dissolved by heating to 90° C. After that, 40 parts of deionized water were dropped to the solution at the temperature over 30 min. Next, 53 parts of dimethylethanolamine were added to the mixture and then the whole was subjected to a reaction by being stirred for 1 hr. Further, 2,350 parts of deionized water were added to the resultant over 1 hr to provide an aqueous dispersion of an ammonium salt group-containing modified epoxy resin (ae-2) having a solid content of about 25%. The resultant resin had a resin acid value of 75 mgKOH/g, a quaternary ammonium salt amount (result based on the electric conductivity titration) of 1.8×10⁻⁴ mol/g, and a weight-average molecular weight of 18,000.

(3) Production of Aqueous Hydrophobic Coating Composition (D) Production Example 5 Aqueous Hydrophobic Coating Composition (D-1)

10 parts (solid content) of a UNIDYNE TG-500S (*1 of Note 2), parts (solid content) of the quaternary ammonium salt group-containing modified epoxy resin (ae-1) obtained in Production Example 3, and 10 parts (solid content) of a MYCOAT 715 (*4 of Note 2) were added, and then deionized water was further added to the mixture to adjust its solid content. Thus, an aqueous hydrophobic coating composition (D-1) having a solid content of 10% was obtained.

Production Examples 6 to 12 Aqueous Hydrophobic Coating Compositions (D-2) to (D-8)

Respective components were sufficiently stirred with a stirring machine in accordance with formulation shown in each of Table 1 and Table 2 below, and then deionized water was added to the mixture to adjust its solid content. Thus, aqueous hydrophobic coating compositions (D-2) to (D-8) each having a solid content of 10% were produced.

TABLE 1 Aqueous hydrophobic coating composition D-1 D-2 D-3 D-4 D-5 D-6 D-7 D-8 Resin (A) having fluorine UNIDYNE 10 — — — —  1  3 20 atom-containing group TG-500S(*1) UNIDYNE — 10 — 10 — — — — TG-580(*2) UNIDYNE — — 10 — 10 — — — TG-581(*3) Quaternary ammonium salt ae-1 90 90 90 — — 90 90 90 group-containing modified ae-2 — — — 90 90 — — — epoxy resin (B) Amino resin (C) MYCOAT 715(*4) 10 10 10 10 10 10 10 10 (Note 1) The ratio of a blended content is represented in a “part(s) by mass” unit in terms of a solid content. (Note 2) (*1)UNIDYNE TG-500S: manufactured by DAIKIN INDUSTRIES, LTD, trade name, water dispersion of fluorine-based resin, solid content: 30 mass % (*2)UNIDYNE TG-580: manufactured by DAIKIN INDUSTRIES, LTD, trade name, water dispersion of fluorine-based resin, solid content: 30 mass % (*3)UNIDYNE TG-581: manufactured by DAIKIN INDUSTRIES, LTD, trade name, water dispersion of fluorine-based resin, solid content: 30 mass % (*4)MYCOAT 715: Nihon Cytec Industries Inc., trade name, methyl-etherified melamine resin, solid content: 80%

Production Examples of Hydrophilic Coating Compositions (E) Production Example 13 Polyvinyl Alcohol Aqueous Solution (e-1)

A DENKA POVAL K-05 (manufactured by DENKI KAGAKU KOGYO KABUSHIKI KAISHA, saponification degree: 99%, polymerization degree: 550) was dissolved in water to provide a polyvinyl alcohol aqueous solution (e-1) having a solid content of 14%.

Production Example 14 Acrylic Resin Aqueous Solution

80 parts of a “JULIMER AC10LP” (polyacrylic acid manufactured by Nihon Junyaku Co., Ltd., weight-average molecular weight: 25,000, acid value: 779 mgKOH/g) were dissolved in 535 parts of a 3% aqueous solution of n-butanol to provide an acrylic resin aqueous solution (e-2) having a solid content of 13%.

Production Example 15 Acrylic Resin Aqueous Solution)

80 parts of a “JULIMER AC10LHP” (polyacrylic acid manufactured by Nihon Junyaku Co., Ltd., weight-average molecular weight: 250,000, acid value: 779 mgKOH/g) were dissolved in 920 parts of a 3% aqueous solution of n-butanol to provide an acrylic resin aqueous solution (e-3) having a solid content of 8%.

Production Example 16 Hydrophilic Coating Composition (E-2)

385 parts of the acrylic resin aqueous solution (e-2) having a solid content of 13% obtained in Production Example 14 were added to 357 parts of the polyvinyl alcohol aqueous solution (e-1) having a solid content of 14% obtained in Production Example 13. Further, 146 parts of a mixed solution (solution containing lithium hydroxide monohydrate at a concentration of 10%) of 14.6 parts of lithium hydroxide monohydrate (LiOH.H₂O) and 131.4 parts of a 3% aqueous solution of n-butanol were added to the mixture so that the neutralization degree of the carboxyl groups of the acrylic resin became 0.6 equivalent, followed by mixing and stirring. Further, 112 parts of a 3% aqueous solution of n-butanol were added to the resultant, and then the contents were mixed and stirred so as to be uniform. Thus, a hydrophilic coating composition (E-2) having a solid content of 10% was obtained. Table 2 shows coating formulation.

Production Example 17 Hydrophilic Coating Composition (E-3)

385 parts of the acrylic resin aqueous solution (e-3) having a solid content of 13% obtained in Production Example 15 were added to 357 parts of the polyvinyl alcohol aqueous solution (e-1) having a solid content of 14% obtained in Production Example 13. Further, 146 parts of a mixed solution (solution containing lithium hydroxide monohydrate at a concentration of 10%) of 14.6 parts of lithium hydroxide monohydrate (LiOH.H₂O) and 131.4 parts of a 3% aqueous solution of n-butanol were added to the mixture so that the neutralization degree of the carboxyl groups of the acrylic resin became 0.6 equivalent, followed by mixing and stirring. Further, 112 parts of a 3% aqueous solution of n-butanol were added to the resultant, and then the contents were mixed and stirred so as to be uniform. Thus, a hydrophilic coating composition (E-3) having a solid content of 10% was obtained. Table 2 shows coating formulation.

TABLE 2 Hydrophilic coating composition E-2 E-3 Polyvinyl alcohol aqueous solution (e-1) 50 50 Acrylic resin aqueous solution (e-2) 50 — Acrylic resin aqueous solution (e-3) — 50 Lithium hydroxide monohydrate (neutralization 0.6 0.6 equivalent) (Note) Contents blended in the components e-1 to e-3 are each represented in a “part (s) by mass” unit in terms of a solid content.

Preparation of Comparative Hydrophobic Coating Composition Comparative Production Example 1 Modified Epoxy Resin Free of Quaternary Ammonium Salt Group

513 parts of a jER828EL (manufactured by Japan Epoxy Resins, Co., Ltd., epoxy resin, epoxy equivalent: about 190, number-average molecular weight: about 380), 287 parts of bisphenol A, 0.3 part of tetramethylammonium chloride, and 89 parts of methyl isobutyl ketone were loaded, and were then subjected to a reaction for about 4 hr while being heated to 140° C. in a stream of nitrogen. Thus, an epoxy resin solution was obtained. The resultant epoxy resin had an epoxy equivalent of 3,700 and a number-average molecular weight of about 17,000.

Next, 667 parts of the solution of the carboxyl group-containing acrylic resin (ca-1) having a solid content of about 30% obtained in Production Example 1 were charged into the resultant epoxy resin solution, and were then uniformly dissolved by heating to 90° C. After that, 40 parts of deionized water were dropped to the solution at the temperature over 30 min. Next, 0.2 part of tetramethylammonium chloride was added to the mixture and then the whole was subjected to a reaction under stirring for 3 hr. Further, a mixture of 2,380 parts of deionized water and 23 parts of 25% ammonia water was added to the resultant over 1 hr to provide an aqueous dispersion of a modified epoxy resin free of any quaternary ammonium salt group having a solid content of about 25%. The resultant resin had a resin acid value of 48 mgKOH/g and a weight-average molecular weight of 24,000.

TABLE 3 Comparative hydrophobic coating composition F-1 F-2 F-3 F-4 F-5 Resin (A) having fluorine UNIDYNE 10 — — — 10 atom-containing group TG-500S(*1) UNIDYNE — 10 — — — TG-580(*2) UNIDYNE — — 10 — — TG-581(*3) LUMIFLON — — — 10 — FE-2320(*5) Quaternary ammonium salt (ae-1) 90 90 90 90 — group-containing modified epoxy resin (B) Modified epoxy resin free of quaternary 90 ammonium salt group (*6) Amino resin (C) MYCOAT 715(*4)  0  0  0 10 10 (Remark 1) The ratio of a blended content is represented in a “part(s) by mass” unit in terms of a solid content. (Remark 2) (*1) to (*4)The resins are identical to those of Table 1. (*5)LUMIFLON FE-2320: manufactured by ASAHI GLASS CO., LTD., trade name, an alternating copolymer of fluoroethylene and vinyl ether (that does not have any perfluoroalkyl group) (*6): The modified epoxy resin of Comparative Production Example 1 (free of any quaternary ammonium salt group)

<Production of Heat Exchanger Using Precoated Fin Material>

(Production of Anticorrosive Fin Substrates a and b for Precoated Fin Materials)

In each of Examples 1 to 4, an aluminum plate material (JIS A 1050) having a plate thickness of 100 μm was used as an aluminum fin material and then the aluminum plate material was subjected to a degreasing treatment. After that, an anticorrosive film was formed by painting each of both surfaces of the aluminum plate material with a chromate-based treatment agent (treatment agent a: manufactured by Nihon Parkerizing Co., Ltd., trade name “ALCHROM 712”) or an organic treatment agent (treatment agent b: manufactured by KANSAI PAINT CO., LTD., trade name “Cosmer 9105”) as an anticorrosive treatment agent through the use of a roll coater. Here, upon preparation of an anticorrosive fin substrate a with the treatment agent a, the substrate was formed by: painting each of both surfaces of the aluminum plate material with the treatment agent a through the use of the roll coater so that the amount of the agent became 20 mg/m² in terms of a Cr amount; and then drying the agent at a peak metal temperature (PMT) of 230° C. for 15 sec. In addition, when the treatment agent b was used, an anticorrosive fin substrate b was formed by: painting each of both surfaces of the aluminum plate material with the treatment agent b through the use of the roll coater so that the thickness of the agent became 1.0 g/m²; and then drying the agent at a PMT of 250° C. for 10 sec.

(Formation of Hydrophilic Films E-1 to E-3 Each Using Hydrophilic Coating Composition)

In each of Example 1 and Comparative Example 9, the top of the anticorrosive film on the anticorrosive fin substrate a was painted with a carboxymethylcellulose-based coating material E-1 (manufactured by Nippon Paint Co., Ltd., trade name “SURFALCOAT 160”) by using a roll coater so that the coating material had a thickness shown in Table 4. Next, the coating material was dried at a PMT of 200° C. for 10 sec to form a hydrophilic film. In addition, in each of Examples 2 and 4, the top of the anticorrosive film on the anticorrosive fin substrate a or b was painted with the coating material E-1 or coating material E-2 shown in Table 2 in the same manner as in the case of Example 1, and then the coating material was dried at a PMT of 230° C. for 10 sec.

(Formation of Crosslinked Hydrophobic Film Using Aqueous Hydrophobic Coating Composition)

After the hydrophilic film E-1 had been formed on the anticorrosive film a, in Example 1, the resultant was painted with the coating material D-1 of the aqueous hydrophobic coating composition shown in Table 1 by using a spray so that the coating material had a thickness shown in Table 4, and in Comparative Example 9, the resultant was painted with the comparative hydrophobic coating composition F-1 shown in Table 3 by using a spray so that the coating material had a thickness shown in Table 4. Next, the coating material was dried at a PMT of 220° C. for 10 sec to produce a precoated fin having a crosslinked hydrophobic film on part of a fin substrate.

In Example 2, after the anticorrosive film a and the hydrophilic film E-2 had been formed, the resultant was painted with the coating material D-1 of the aqueous hydrophobic coating composition shown in Table 1 by using a spray so that the coating material had a thickness shown in Table 4, followed by drying under the conditions of Example 1 to produce a precoated fin having a crosslinked hydrophobic film on part of its surface as a heat exchange fin of Example 2.

In each of Example 3 and Comparative Example 10, after the anticorrosive film a had been formed, the resultant was painted with the coating material D-2 of the aqueous hydrophobic coating composition shown in Table 1 in Example 3, or the comparative hydrophobic coating composition F-2 shown in Table 3 in Comparative Example 10, by using a roll coater so that the coating material had a thickness shown in Table 4, followed by drying under the conditions of Example 1.

In Example 4, after the anticorrosive film b and the hydrophilic film E-3 had been formed, the resultant was painted with the coating material D-2 of the aqueous hydrophobic coating composition shown in Table 1 by using a roll coater so that the coating material had a thickness shown in Table 4, followed by drying under the conditions of Example 1.

(Production of Heat Exchanger Using Precoated Fin)

The precoated fin of each of Examples 1 and 2 in which the crosslinked hydrophobic film having a frost formation-suppressing effect had been formed on part of the fin substrate was cut into a piece measuring 500 by 25 by 0.1 mm and then subjected to press working with 2 rows×12 rows of collar portions to provide a heat exchange fin. The heat exchange fins were laminated so as to coincide with the collar portions, and then a copper tube (JIS-C1220, outer diameter: 7 mm, wall thickness: 0.3 mm) was inserted into the collar portions of the formed laminate. Next, the copper tube was expanded with a mandrel to join the collar portions mechanically. Thus, a cross fin tube-type heat exchanger (having external dimensions measuring 500 mm by 25 mm by 250 mm) of each of Examples 1 and 2 including the heat exchange fin having the crosslinked hydrophobic film on part of its surface was produced.

In Example 3, a heat exchanger was produced in the same manner as in Example 1 by using a precoated fin in which a crosslinked hydrophobic film having a frost formation-suppressing effect had been formed on a fin substrate. Next, a cross fin tube-type heat exchanger of Example 3 including a heat exchange fin having the crosslinked hydrophobic film on part of its surface was produced in the same manner as in Example 1 by immersing the heat exchanger in tap water at 40° C. for 30 min and drying the heat exchanger as a post-treatment.

In Example 4, a heat exchanger was produced in the same manner as in Example 1 by using a precoated fin in which a crosslinked hydrophobic film having a frost formation-suppressing effect had been formed on a fin substrate. Next, a cross fin tube-type heat exchanger of Example 4 including a heat exchange fin having the crosslinked hydrophobic film on part of its surface was produced in the same manner as in Example 1 by subjecting the heat exchanger to spray washing with industrial water at 80° C. for 1 min and drying the heat exchanger as a post-treatment.

In Comparative Example 9, a heat exchanger was produced in the same manner as in Example 1 by using a precoated fin in which a hydrophobic film had been formed on part of a fin substrate.

In Comparative Example 10, a cross fin tube-type heat exchanger was produced in the same manner as in Example 1 by using a precoated fin in which a hydrophobic film had been formed on a fin substrate. Next, a cross fin tube-type heat exchanger was produced in the same manner as in Example 1 by subjecting the heat exchanger to spray washing with tap water at 80° C. for 1 min and drying the heat exchanger as a post-treatment.

Production of Heat Exchanger Using Corrugated Fin Examples 5 to 12 and Comparative Examples 1 to 8 Heat Exchanger Using Corrugated Fin and Formation of Hydrophilic Film with Flux

A heat exchanger using a corrugated fin is of a parallel-flow heat exchange type constructed of a porous extruded flat tube as a flat flow channel tube, the corrugated fin, and a header pipe made of aluminum.

In each of Examples 5 to 8 and Comparative Examples 1 to 8, the porous extruded flat tube (JIS A1050 alloy, width: 16 mm, thickness: 0.93 mm, wall thickness: 0.35 mm) and the corrugated fin formed of a clad brazing sheet (JIS A4343 alloy/JIS A3003 alloy/JIS A4343 alloy, thickness: 0.9 mm, fin height: 7.9 mm, fin width: 16 mm) were laminated, and then the header pipe made of aluminum was set at each of both ends of the laminate, followed by restriction with a jig made of SUS. After that, a flux made of a complex compound of KAlF₄ and K₃AlF₆ was applied to the laminate with a spray, and was then dried at 150° C. for 5 min. The average application amount of the flux after the drying was 5 g/m² in the case of each of Examples 5 and 6, 15 g/m² in the case of each of Examples 7 and 8, 3 g/m² in the case of each of Comparative Examples 1 and 2, and 9 g/m² in the case of each of Comparative Examples 3 to 8.

Next, the resultant was subjected to a temperature increase and heating in a mesh belt-type continuous furnace having an inert atmosphere muffle replaced with an N₂ gas, followed by brazing at 600° C. After the flat tube and the fin, and the flat tube and the header pipe had been joined to each other by the brazing, the resultant was cooled to normal temperature in a continuous brazing furnace. After the brazing, a section of the fin material was observed. As a result, it was found that a film formed of the flux had irregularities, in each of Examples 5 and 6, a thick portion had a thickness of 10 μm and a thin portion had a thickness of 0.5 μm, in each of Examples 7 and 8, a thick portion had a thickness of 35 μm and a thin portion had a thickness of 2 μm, in each of Comparative Examples 1 and 2, a thick portion had a thickness of 4 μm and a thin portion had a thickness of 0.4 μm, and in each of Comparative Examples 3 to 8, a thick portion had a thickness of 15 μm and a thin portion had a thickness of 1.2 μm. The heat exchanger made of an aluminum alloy after the brazing was washed with tap water and dried as a pretreatment for the painting.

(Anticorrosive Treatment and Production of Heat Exchanger Including Anticorrosive Fin Substrate c)

In each of Examples 5 and 6, and Comparative Examples 6 and 7, after the painting pretreatment, the heat exchanger to which the corrugated fin (heat exchange fin) had been brazed was immersed in a bath, which contained a 2% solution of an ALSURF 375 manufactured by Nippon Paint Co., Ltd. warmed to 40° C., for 1 min and lifted. After that, the heat exchanger was sufficiently washed with water and dried at 50° C. for 1 min to produce a heat exchanger including an anticorrosive fin substrate c.

In each of Examples 7 and 8, and Comparative Examples 1 to 5 and 8, no anticorrosive film was formed.

(Formation of Crosslinked Hydrophobic Film)

Next, in each of Examples 5 to 8, each of the coatings D-3 to D-6 of the aqueous hydrophobic coating compositions shown in Table 1 was applied through immersion so as to have a thickness shown in Table 4, and was then drained off, followed by drying in a continuous drying furnace at 160° C. for 30 min.

In addition, in each of Comparative Examples 1 to 7, each of the coating material D-1 of the aqueous hydrophobic coating composition shown in Table 1, and the aqueous hydrophobic coating compositions F-1 to F-5 of Comparative Examples shown in Table 3 was applied through immersion so as to have a thickness shown in Table 4, and was then drained off, followed by drying in a continuous drying furnace at 160° C. for 30 min.

In Comparative Example 8, the coating material of the aqueous hydrophobic coating composition was not applied and a state after the brazing was maintained.

(Post-Treatment)

Next, in Example 5, no post-treatment was performed, and in Example 6, after having been immersed in a 1% solution of caustic soda at 50° C. for 30 sec and lifted, the heat exchanger was sufficiently washed with tap water and dried as a post-treatment. Further, in Example 7, the heat exchanger was washed with tap water at 60° C. for 30 min as a post-treatment. Further, in Example 8, after having been immersed in a 1% solution of sulfuric acid at 40° C. for 30 sec and lifted, the heat exchanger was sufficiently washed with tap water and dried as a post-treatment. Thus, a parallel flow-type heat exchanger of each of Examples 5 to 8 including a heat exchange fin having a crosslinked hydrophobic film on part of its surface was produced.

In each of Comparative Examples 3 and 7, after having been immersed in tap water at 80° C. for 1 min and lifted, the heat exchanger was sufficiently washed with water and dried as a post-treatment. In any other comparative example, no post-treatment was performed. Thus, a parallel flow-type heat exchanger of each of Comparative Examples 1 to 8 was produced.

Examples 9 and 10 Heat Exchanger Using Corrugated Fin and Formation of Hydrophilic Film with Flux

In each of Examples 9 and 10, a porous extruded flat tube (width: 16 mm, thickness: 1.93 mm, wall thickness: 0.35 mm) obtained by adding 0.4% of Cu, 0.03% of Zr, and 0.1% of Ti to a JIS A1050 alloy was used as a flat flow channel tube. The surface of the flat flow channel tube was immersed in a solution obtained by turning Si metal powder having an average particle diameter of 10 μm or less, a mixed flux of K₂AlF₅.H₂O and KZnF₃, and an acrylic resin as a binder into a slurry in an industrial alcohol, and was then dried at 250° C. for 3 min. Formed on the surface after the drying was an Si/flux mixed film containing the Si metal powder having an average application amount of 4 g/m², the flux having an average application amount of 10 g/m², and the binder having an average application amount of 3 g/m².

The porous extruded flat tube having the Si/flux mixed film formed on its surface and a natural corrugated fin (thickness: 0.9 mm, fin height: 7.9 mm, fin width: 16 mm) obtained by adding 1.5% of Zn to a JIS A3003 alloy were laminated, and then a header pipe made of aluminum was set at each of both ends of the laminate, followed by restriction with a jig made of SUS. After that, the resultant was subjected to a temperature increase and heating in a mesh belt-type continuous furnace having an inert atmosphere muffle replaced with an N₂ gas, followed by brazing at 595° C. After the flat tube and the fin, and the flat tube and the header pipe had been joined to each other by the brazing, the resultant was cooled to normal temperature in a continuous brazing furnace. After the brazing, a section of the fin material was observed. As a result, it was found that the Si/flux film of the flat flow channel tube spread over the corrugated fin material, the fin material had irregularities, and a thick portion had a thickness of 5 μm and a thin portion had a thickness of 0.5 μm. The heat exchanger made of an aluminum alloy after the brazing was washed with tap water and dried as a pretreatment for the painting.

(Anticorrosive Treatment and Production of Heat Exchanger Including Anticorrosive Fin Substrate c)

In each of Examples 9 and 10, after the painting pretreatment, a heat exchanger including the anticorrosive fin substrate c was produced in the same manner as in each of Examples 5 and 6 for forming an anticorrosive film.

(Formation of Crosslinked Hydrophobic Film)

Next, the heat exchanger of each of Examples 9 and 10 was painted with the coating material D-7 of the aqueous hydrophobic coating composition shown in Table 1 through immersion so that the coating material had a thickness shown in Table 4, and then the coating material was dried in a continuous drying furnace at 160° C. for 30 min.

(Post-Treatment)

Next, in Example 9, no post-treatment was performed, and in Example 10, after having been immersed in tap water at 80° C. for 30 sec and lifted, the heat exchanger was sufficiently washed with tap water and dried as a post-treatment. Thus, a parallel flow-type heat exchanger of each of Examples 9 and 10 including a heat exchange fin having a crosslinked hydrophobic film on part of its surface was produced.

Examples 11 and 12 Heat Exchanger Using Corrugated Fin and Formation of Hydrophilic Film with Flux

In each of Examples 11 and 12, a porous extruded flat tube (width: 16 mm, thickness: 1.93 mm, wall thickness: 0.35 mm) obtained by adding 0.40 of Cu, 0.03% of Zr, and 0.1% of Ti to a JIS A1050 alloy was used as a flat flow channel tube. The surface of the flat flow channel tube was immersed in a solution obtained by turning Si metal powder having an average particle diameter of 10 μm or less, a mixed flux of K₂AlF₆ and KZnF₃, and an acrylic resin as a binder into a slurry in an industrial alcohol, and was then dried at 250° C. for 3 min. Formed on the surface after the drying was an Si/flux mixed film containing the Si metal powder having an average application amount of 4 g/m², the flux having an average application amount of 10 g/m², and the binder having an average application amount of 3 g/m².

The porous extruded flat tube having the Si/flux mixed film formed on its surface and a natural corrugated fin (thickness: 0.9 mm, fin height: 7.9 mm, fin width: 16 mm) obtained by adding 1.5% of Zn to a JIS A3003 alloy were laminated, and then a header pipe made of aluminum was set at each of both ends of the laminate, followed by restriction with a jig made of SUS. After that, a flux made of a complex compound of KAlF₄ and K₃AlF₆ was applied to the laminate with a spray, and was then dried at 150° C. for 5 min. The average application amount of the flux after the drying was 7 g/m².

Next, the resultant was subjected to a temperature increase and heating in a mesh belt-type continuous furnace having an inert atmosphere muffle replaced with an N₂ gas, followed by brazing at 595° C. After the flat tube and the corrugated fin, and the flat tube and the header pipe had been joined to each other by the brazing, the resultant was cooled to normal temperature in a continuous brazing furnace.

After the brazing, a section of the corrugated fin was observed. As a result, it was found that the corrugated fin had irregularities derived from the flux film, and a thick portion had a thickness of 15 μm and a thin portion had a thickness of 2 μm. The heat exchanger made of an aluminum alloy after the brazing was washed with tap water and dried as a pretreatment for the painting.

(Anticorrosive Treatment)

In each of Examples 11 and 12, no anticorrosive film was formed.

(Formation of Crosslinked Hydrophobic Film)

Next, the heat exchanger of each of Examples 11 and 12 was painted with the coating material D-8 of the aqueous hydrophobic coating composition shown in Table 1 through immersion so that the coating material had a thickness shown in Table 4, and then the coating material was dried in a continuous drying furnace at 160° C. for 30 min.

(Post-Treatment)

Next, in Example 12, after having been immersed in industrial water at normal temperature for 30 min and lifted, the heat exchanger was sufficiently washed with tap water and dried as a post-treatment. Thus, a parallel flow-type heat exchanger of each of Examples 11 and 12 including a heat exchange fin having a crosslinked hydrophobic film on part of its surface was produced.

FIG. 1 illustrates the heat exchanger made of an aluminum alloy obtained in each of Examples 5 to 12 and Comparative Examples 1 to 8 by joining a corrugated fin 5 and an extruded flat tube 4, and the extruded flat tube 4 and a header pipe 3, to each other through brazing, and then cooling the resultant to normal temperature in a continuous brazing furnace. In FIG. 1, one of the pair of header pipes 3 is provided with a heating medium-introducing port 1 and the other is provided with a discharge port 2.

It should be noted that in the following examples and comparative examples, the measurement of the water contact angles of a crosslinked hydrophobic film and a hydrophilic film, the measurement of the area ratio of the crosslinked hydrophobic film, and the confirmation of a frost formation-suppressing effect were performed by the following methods.

(Measurement of Water Contact Angle)

In each of Examples and Comparative Examples, an aluminum fin material measuring 7 cm by 15 cm was prepared for contact angle measurement, and then the formation of an anticorrosive film, a hydrophilic film, and a crosslinked hydrophobic film, and a post-treatment were performed in the same manner as in Examples except that the portion painted by using a roll coater was painted by using a bar coater. Thus, a test piece of the hydrophilic film, a test piece having the crosslinked hydrophobic film on the hydrophilic film, a test piece having the hydrophilic film on the anticorrosive film, or a test piece having the hydrophilic film formed on the anticorrosive film and having the crosslinked hydrophobic film thereon was produced. 2 μL of pure water were dropped on the hydrophobic or hydrophilic film to be subjected to the measurement of the test piece placed horizontally and then the contact angle of a water droplet formed on the film of the test piece was measured with a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd.: CA-A).

(Measurement of Area Ratio of Crosslinked Hydrophobic Film)

The fin material having a size measuring about 10 by 10 mm was cut out of the heat exchanger produced in each of Examples 1 to 12 and Comparative Examples 1 to 7, the carbon (C) mapping of the surface of the film was performed with an X-ray microanalyzer (EPMA), and the area ratio of carbon (C) in an area measuring 5 by 5 mm2 was calculated by image analysis.

(Evaluation of Heat Exchanger)

Next, a 50-wt % aqueous solution of propylene glycol was introduced as a refrigerant into the test heat exchanger of each of Examples 1 to 12 and Comparative Examples 1 to 8 thus produced. The refrigerant was circulated in a thermostatic chamber having a chamber temperature of 2° C. and a humidity RH of 90% or more under the conditions of a refrigerant temperature of −6° C. and a refrigerant flow rate of 1 L/min, and then the heat exchanger was operated for 45 min, followed by the observation of a frost formation state in the heat exchange fin of each test heat exchanger. In addition, after the frost formation, a defrosting operation was performed with the refrigerant at 30° C. for 3 min, followed by the observation of the presence or absence of the formation of a bridge by melt water (or condensed water) produced between heat exchange fins.

The frost formation-suppressing effect was evaluated as described below. A time period required for the formation of frost on the entire surface was measured and the evaluation was performed by the following criteria: x: the case where the time period was less than 15 min, Δ: the case where the time period was 15 min or more and less than 30 min, 0: the case where the time period was 30 min or more and less than 45 min, and ⊚: the case where no frost formation occurred even after a lapse of 45 min. In addition, a condensed water-removing effect was evaluated as described below. The state of adhesion of the melt water (or condensed water) between the fins after the defrosting operation was observed and the evaluation was performed by the following criteria: x: the case where the bridge occurred on substantially the entire surface, Δ: the case where the bridge occurred on part of the surface, and ∘: the case where the occurrence of the bridge was not observed.

TABLE 4 Example 1 2 3 4 5 6 7 8 9 10 11 Kind of fin substrate a a a b c c — — c c — Hydrophilic Kind of coating E-1 E-2 — E-3 — — — — — — — surface material Thickness min. 1.1 0.7 — 0.5 0.5 0.5 2.0 2.0 0.5 0.5 2.0 (μm) max. 1.5 1.0 — 0.8 10 10 35 35 5 5 15 Water contact 5 15 35 10 27 15 10 7 32 21 8 angle (°) Hydrophobic Kind of coating D-1 D-1 D-2 D-2 D-3 D-4 D-5 D-6 D-7 D-7 D-8 surface material Thickness (μm) 0.7 0.4 0.4 1.0 0.7 1.0 0.2 5.0 0.2 1.0 2.5 Water contact 101 100 100 105 105 103 100 108 100 105 108 angle (°) Post-treatment Absent Absent Water Water Absent Alkali Water Acid Absent Water Absent washing washing washing washing washing washing Area of crosslinked hydrophobic 42 75 60 52 43 25 54 38 21 39 45 film (%) Frost formation-suppressing ⊚ ⊚ ⊚ ⊚ ⊚ ◯ ⊚ ⊚ ◯ ⊚ ⊚ effect Condensesd water-removing effect ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Example Comparative Example 12 1 2 3 4 5 6 7 8 9 10 Kind of fin substrate — — — — — — c c — a a Hydrophilic Kind of coating — — — — — — — — — E-1 — surface material Thickness min. 2.0 0.5 0.5 1.2 1.2 1.2 1.2 1.2 1.2 1.5 — (μm) max. 15 4 4 15 15 15 15 15 15 1.8 — Water contact 5 5 5 7 7 7 7 7 7 5 35 angle (°) Hydrophobic Kind of coating D-8 D-1 D-1 F-1 F-2 F-3 F-4 F-5 — F-1 F-2 surface material Thickness (μm) 0.8 6 0.01 0.2 2.0 5.0 2.0 1.0 — 0.2 2.0 Water contact 100 100 70 95 80 100 105 100 — 95 80 angle (°) Post-treatment Water Absent Absent Water Absent Absent Absent Water Absent Absent Water washing washing washing washing Area of crosslinked hydrophobic 70 95 5 2 25 70 65 5 — 51 70 film (%) Frost formation-suppressing ⊚ ⊚ X X X Δ X X X X X effect Condensed water-removing effect ◯ X ◯ Δ X X X X ◯ ◯ X

REFERENCE SIGNS LIST

1 . . . heating medium-introducing port, 2 . . . heating medium-discharging port, 3 . . . header pipe, 4 . . . extruded flat tube, 5 . . . corrugated fin. 

1. A heat exchanger, comprising a heat exchange fin having a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy, and a crosslinked hydrophobic film having a frost formation-suppressing effect and a hydrophilic film formed on a surface of the fin substrate, wherein: an area occupied by the crosslinked hydrophobic film in a square area measuring 10 mm by 10 mm at an arbitrary position on a surface of the heat exchange fin is 10 to 90%; and the crosslinked hydrophobic film is formed of an aqueous hydrophobic coating composition containing a resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) in which a solid content of the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group is 1 to 30 parts by mass with respect to 100 parts by mass of a total of solid contents of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C).
 2. A heat exchanger according to claim 1, wherein the hydrophilic film comprises an inorganic film.
 3. A heat exchanger according to claim 1 or 2, wherein the crosslinked hydrophobic film is formed on the hydrophilic film.
 4. A heat exchanger according to claim 1 or 2, wherein the heat exchange fin comprises a corrugated fin.
 5. A heat exchanger according to claim 4, wherein the hydrophilic film comprises a film formed by a brazing step.
 6. A heat exchanger according to claim 1 or 2, wherein the crosslinked hydrophobic film is formed by baking the aqueous hydrophobic coating composition after application thereof and has a thickness of 0.02 to 5.0 g/m².
 7. A heat exchanger according to claim 1 or 2, wherein the crosslinked hydrophobic film formed in part of the heat exchange fin is nonuniform and spotted.
 8. A heat exchanger according to claim 2, wherein the crosslinked hydrophobic film formed in part of the heat exchange fin is formed on the hydrophilic film, and the crosslinked hydrophobic film and the hydrophilic film form a sea-island structure.
 9. A method of producing a heat exchanger including a heat exchange fin in which a crosslinked hydrophobic film having a frost formation-suppressing effect is formed on an entirety or part of a surface of a fin substrate formed of an aluminum plate material formed of aluminum or an aluminum alloy, the method comprising: applying, to the entirety or part of the surface of the fin substrate, an aqueous hydrophobic coating composition containing a resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group, a quaternary ammonium salt group-containing modified epoxy resin (B), and an amino resin (C) in which a solid content of the resin (A) having at least one kind of fluorine atom-containing group selected from the group consisting of a perfluoroalkyl group and a perfluoroalkenyl group is 1 to 30 parts by mass with respect to 100 parts by mass of a total of solid contents of the quaternary ammonium salt group-containing modified epoxy resin (B) and the amino resin (C), followed by baking of the composition to form the crosslinked hydrophobic film; and subjecting the crosslinked hydrophobic film to a post-treatment with one or two or more kinds of post-treatment liquids selected from water, an acid solution, and an alkaline solution after the formation of the crosslinked hydrophobic film. 